Many designs for earth retaining walls exist today. Wall designs must account for lateral earth and water pressures, the weight of the wall, temperature and shrinkage effects, and earthquake loads. One design type, known as mechanically stabilized earth retaining walls, employs either metallic or polymeric tensile reinforcements in the soil mass. The tensile reinforcements connect the soil mass to modular precast concrete members. The members create a visual vertical facing.
The polymeric tensile reinforcements typically used are elongated lattice-like structures referred to herein as grids. The grids have elongated ribs which connect to transversely aligned bars thereby forming elongated apertures between the ribs. The modular precast concrete members may be in the form of blocks or panels that stack on top of each other to create the vertical facing.
Various connection methods are used during construction of earth retaining walls to interlock the blocks or panels with the grids. One known retaining wall has blocks with bores extending inwardly within their top and bottom surfaces. The bores receive dowels or pins. After a first tier of blocks have been positioned laterally along the length of the wall, the dowels are inserted into the bores of the upper surfaces of the blocks. Edges of grids are placed on the tier so that each of the dowels extends through an aperture. This connects the wall to the grids. The grids extend laterally from the blocks. The dowels are spaced apart such that not every aperture in the grid receives a dowel. Typically, there are several open apertures between each dowel. When the second tier of blocks is positioned, the upwardly extending dowels fit within the bores of the bottom surfaces of the blocks. Once the earth is backfilled over the grids, the load of the earth is distributed at the dowel to the grid connection points. The strength of the grid-to-wall connection is generated by the friction between the block surfaces and the grid and by the linkage between the aggregate trapped in the wall and the apertures of the grid. The magnitude of these two contributing factors varies with workmanship of the wall, normal stresses applied by the weight of the wall above the connection, and by the quality and size of the aggregate.
In another known retaining wall, an upper surface of blocks includes projections and a lower surface of blocks includes cavities. The projections are wider than the apertures in the grids. Enlarged openings are formed by severing several ribs that define adjacent apertures. The projections of a first tier of blocks receive the enlarged openings of the grids. The cavities in the second tier of blocks then enclose the projections in the first tier.
The specifications of earth retaining walls are based upon the strength of the interlocking components and the load created by the backfill. Once the desired wall height and type of ground conditions are known, the number of grids and positioning of them is determined dependent upon the load capacity of the interlocking components. In walls of the type having a dowel construction, the load capacity is a function of the strength of the portion of the concrete block surrounding the dowels. In walls of the type having projections, the load capacity is a function of the strength of the concrete block portion forming the projections.
In both instances, the load of the backfill is concentrated at the point of interlock between either the dowels or projections and the grid apertures. In neither case is the full strength of the grid apertures being utilized since several apertures are void of connecting dowels or the apertures have been destroyed by severing the ribs between apertures. Thus, these walls are limited in the carrying load on the connections to the grid. Transferring the load over more transversely aligned bars facilitates larger loads. Also, the load would be absorbed by the grids with less concentrated stress on the grids and on the portion of the block forming the connection.
Thus, there exists a need for a mechanically stabilized earth retaining wall having a connection between soil reinforcement elements and individual wall units which utilizes the entire design strength of the grids, which evenly distributes the load of the backfill across the length of the grids sufficient to meet the design strength of the grids, and which minimizes the stress around the area of the wall unit that absorbs the load. Accordingly, it is to the provision of such an improved mechanically stabilized earth retaining walls that the present invention is directed.